1. Field of the Invention
The present invention relates to toner residual amount detection of an electrophotographic image forming apparatus.
2. Description of the Related Art
There is known a technology of detecting a toner residual amount in an electrophotographic image forming apparatus. In regard to this technology, a large number of inventions have been filed for application, and the following related art is a typical example.
An LED is installed on one side surface at a predetermined position of a toner replenishing tank and a photodiode is installed on the corresponding other side surface. When the toner replenishing tank has sufficient toner inside and the contained toner reaches above the installation position of the LED, the photodiode does not output an output signal. When the residual toner reaches below the installation position of the LED, the photodiode outputs an output signal. Thus, it is determined whether the toner residual amount is large or small based on the presence/absence of an output signal from the photodiode, for example, such a technology is disclosed in Japanese Patent Application Laid-Open No. H05-027593.
Japanese Patent Application Laid-Open No. H05-027593, does not disclose a countermeasure against the malfunction of a toner residual amount detecting unit and the contamination of an inside the toner replenishing tank. Therefore, there is a risk in that a toner residual amount may be detected erroneously. Thus, in the technology of Japanese Patent Application Laid-Open No. H05-027593, a toner residual amount may not be detected reliably. There is a fear in that a carrier adheres to a photosensitive drum after a continuous use under a toner absence state, which may influence an image forming apparatus.